Muscle strength is the key part of normal body functioning. It can be measured in a lot of ways, but the most common way is through manual muscle testing. Because it is subjective test, manual muscle testing is not considered enough reliable for demanded cases. Today there are quality dynamometers who have the option of more accurate measurements than manual muscle testing. Of these dynamometers, isokinetic diagnostic is higlighted as on of the most reliable and precize metering methods. This paper describes the benefits of isokinetic diagnostic as a diagnostic method over the other two methods and it explains the application of isokinetics for rehabilitation purposes.